Williams, the 1999 U.S. Open champion and runner-up to older sister Venus there last year, was scheduled to play Monday against 1994 Wimbledon champion Conchita Martinez.

Agassi was scheduled to start here Tuesday.

"I'm worried about the state of it and what it might mean" for his career, the 31-year-old Agassi said an hour before the tournament began.

"The pain was bad and fairly familiar," he said, adding that trying to play through pain led to surgery on the wrist in 1993.

He planned to return immediately to the United States for assessment and treatment.

Agassi said he hurt the wrist in the first set of a 7-6 (6), 6-7 (6), 6-3 loss to Pete Sampras on Saturday in the final of the Kooyong Classic, an exhibition warmup for the open.

But after the match and again on Sunday, he talked of being in excellent shape and confident for his title defense.

Sunday night, he said, he had knots in his stomach when he called Open director Paul McNamee to arrange a session with the tournament doctor.

"It was a decision I labored over," said Agassi, who was seeded third. "It's very rare in your career when you wouldn't want to be the defending champion but this is one of them."

His replacement in the draw, 20-year-old Irakli Labadze of the former Soviet republic of Georgia, beat Agassi in the first round of a tournament in Shanghai last September, saving a set point in each set. Labadze, ranked No. 104, failed to qualify here but now will be playing in his first Grand Slam tournament, facing qualifier Byron Black of Zimbabwe on Tuesday.

Agassi won the Open in 2000 and 2001 and had a chance to become the first man to win three consecutive Australian Opens since Roy Emerson won five in a row from 1963-67.

Three of Agassi's seven Grand Slam titles came in Australia.

"I love the conditions, I love everything the court has to offer for my game," he said Sunday. "It's definitely brought out some of my best tennis."

Agassi had been in the same half of the draw as No. 1 Lleyton Hewitt, Sampras, Marat Safin and Andy Roddick. They start play Tuesday.

Monday's first featured men's match had French Open champion Gustavo Kuerten against Julien Boutter of France.

Hewitt, voted the 2001 ATP Player of the Year, gives the home crowd hope for the first Australian winner here since Mark Edmondson in 1976.

At 20 years, 8 months, he was the youngest year-end No. 1 since the ATP rankings started in 1973.

He's recovering from chicken pox, although he won an exhibition match against Todd Martin on Friday.

Among the women, Venus Williams came to last year's Australian Open as the reigning Wimbledon and U.S. Open champion, and struggled just to reach the semifinals.

This year, she has the same two titles in hand and the same prominent rivals in her half of the draw -- but less offseason rust showing.

By beating Justine Henin last weekend to win a tuneup tournament, Williams won her 14th straight match against a top-10 player and 20th in a row overall.

Williams was in the first center-court women's match Monday, meeting Ansley Cargill, an American qualifier ranked 230th. Williams needed three sets to get by a qualifier in last year's opening round.

She skipped the Sydney tournament where sister Serena hurt her ankle.

For Martina Hingis, the Australian Open champion in 1997-99 and a finalist the last two years, Sydney was her first tournament since an ankle injury forced a three-month layoff and she lost the No. 1 ranking after 73 consecutive weeks.